Preheat your oven to 425°F (220°C) and line a large sheet pan with parchment paper for easy cleanup.
In a large bowl, combine olive oil, lemon juice, dried oregano, garlic powder, paprika, salt, and pepper. Whisk to form a marinade.
Add the chicken thighs to the marinade, coating them thoroughly. Allow them to marinate for at least 15 minutes (or up to 2 hours in the refrigerator for more flavor).
Arrange the marinated chicken on one side of the sheet pan. Add the sliced red onion, bell pepper, and halved cherry tomatoes to the other side. Drizzle with a bit more olive oil and season with salt and pepper.
Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (75°C) and the vegetables are tender.
While the chicken and veggies are baking, warm the pita breads in a microwave or on a dry skillet for a minute on each side.
Once everything is cooked, remove from the oven. Slice the chicken into strips.
To assemble the gyros, place a portion of chicken, roasted vegetables, and a generous dollop of tzatziki sauce inside each pita.
Garnish with fresh parsley for an extra touch of flavor and color.
Notes
Serve the gyros on a wooden board, surrounded by extra tzatziki and fresh parsley. Optionally, include lemon wedges for a fresh squeeze on top before enjoying!